The present invention relates to a coupler apparatus for a rotation sensor for detecting rotation of a rotating shaft such as a kingpin in vehicles.
Generally, in forklifts, pivoting of a rear axle is limited so that the vehicle body does not incline excessively from centrifugal force when turning. The pivoting of the rear axle is controlled according to, for example, the velocity of the vehicle and the steering angle. Japanese Examined Patent Publication No. 4-24270 describes a method for detecting the steering angle. In this publication, a displacement sensor attached to a steering cylinder detects the piston displacement, and the steering angle is calculated from the displacement. However, using this method, it is difficult to obtain the steering angle. Therefore, the present applicant devised a potentiometer located on an upper bracket of an axle beam for detecting the pivoting angle of a kingpin and for obtaining the steering angle from the detected pivoting angle.
As shown in FIG. 21, a potentiometer 52 for detecting the rotation of the kingpin 10 is mounted on the upper bracket 51 supporting a kingpin 50 in a rear axle beam. The potentiometer 52 is fixed to the upper bracket 51 through a sensor support plate 54 so that the potentiometer 52 is located above a bearing hole 53 in which the kingpin 50 is supported. The potentiometer 52 is fixed to the support late 54 by screws (not shown), and the support plate 54 is fixed to an upper bracket 51 by bolts (not shown). An input shaft 55 of the potentiometer 52 passes through the through hole 54a toward the kingpin 50, and a body 56 of the potentiometer 52 is fixed to the support plate 54. The axis of the input shaft 55 is aligned with the axis of the kingpin 50. A coupling portion 55a, the cross section of which is D-shaped, is formed at the distal end of the input shaft 55, and the coupling portion engages a D-shaped coupling hole 57 in the upper end of the kingpin 50. This prevents relative rotation between the input shaft 55 and the kingpin 50.
Dimensional inaccuracy of parts occurs, and this may offset the axis of the input shaft 55 from the axis of the kingpin 50. Roller bearings wear after a long period of use, and this may cause the axis of the kingpin 50 to shift from the original position at the center of the bearing hole 53. This may also offset the axis of the input shaft 55 from the axis of the kingpin 50. As a result, a radial force is applied from the kingpin 50 to the input shaft 55, which may degrade the detection sensitivity and durability of the potentiometer 52. If the radial force becomes excessive, the potentiometer 52 may be damaged.
It is possible to prevent the input shaft 55 from receiving the radial force from the kingpin 50 by providing a clearance between the kingpin 50 and the input shaft 55. However, this may cause slack between the input shaft 55 and the kingpin 50 in the rotational direction and may degrade detection sensitivity.